I saw a guy making Qi receiver module with ATTiny13A: Qi wireless power receiver from scratch.
In his circuit, secondary shorted through capacitors to ground to send data.
My question is how transmitter side (base) reads this data?
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When the output is loaded, the power draw to the transmitter increases because of coupling between the coils.
The resulting current/voltage fluctuation is monitored, demodulated and read as data. The data flow is only possible from (power) receiver to transmitter.
You can find a lot more information in this application note from NXP/Freescale entitled Demodulating Communication Signals of Qi-Compliant Low-Power Wireless Charger Using MC56F8006 DSC,
The tuned LC high Q resonance at 100kHz is modulated in bi-phase to target where the resonant coils can receive the modulated carrier. The receiver then drives the gate to return a ping back and then an ID response with power demand.
When the mutual coupling is good with Gap<< diameter efficient low loss carrier power transfer is possible to a diode bridge cap not a 10uH cap. The buildup of voltage depends on this C ratio of nF to uF requiring 1000 cycles for the time constant if 22nF/2nF to 10uF ~1100:1 cycles
Coil inductance and high tolerance caps may require tuning.
The Q is thus XL(100kHz) /RdsOn/2.